During manufacturing, paper goods often have some form of coating applied thereon such as adhesives or inks which usually require some type of curing process. Examples of such coated paper goods include magazines, labels, stickers, prints, etc. The coatings are typically applied to the paper when the paper is in the form of a continuously moving web of paper. Current manufacturing methods of curing coatings on a moving web include subjecting the coatings to heat, UV light or electron beams.
When curing coatings on a moving web with electron beams, an electron beam system is usually positioned over the moving web. If the web has a large width, for example 50 inches or more, an electron beam system consisting of multiple electron beam devices is sometimes used to irradiate the full width of the web. The electron beam devices in such a system are staggered relative to each other resulting in a staggered pattern of electron beams that are separated from each other and provide full electron beam coverage across the width of the web only when the web is moving. The staggered arrangement is employed because, if multiple electron beam devices were positioned side by side, the electron beam coverage on a moving web would be interrupted with gaps between electron beams. A staggered arrangement is depicted in application Ser. No. 08/778,037, filed Jan. 2, 1997, now U.S. Pat. No. 5,962,995, the teachings of which are incorporated by reference herein in their entirety.
A drawback of an electron beam system having staggered electron beam devices is that such a system can require a relatively large amount of space, particularly in situations where multiple sets of staggered electron beam devices are positioned in series along the direction of the moving web for curing coatings on webs moving at extremely high speeds (up to 3000 ft/min). This can be a problem in space constrained situations.
One aspect of the present invention is directed towards an electron beam accelerator device which can be mounted adjacent to one or more other electron beam accelerator devices along a common axis to provide overlapping continuous electron beam coverage along the axis. This allows wide electron beam coverage while remaining relatively compact in comparison to previous methods. The present invention provides an electron accelerator including a vacuum chamber having an outer perimeter and an electron beam exit window. The exit window has a central region and a first end region. An electron generator is positioned within the vacuum chamber for generating electrons. The electron generator and the vacuum chamber are shaped and positioned relative to each other to accelerate electrons in an electron beam out through the exit window. The Electrons pass through the central region of the exit window substantially perpendicular to the exit window and through the first end region of the exit window angled outwardly relative to the exit window. At least a portion of outwardly angled electrons are directed beyond the outer perimeter.
In preferred embodiments, the exit window has a second end region opposite to the first end region. Electrons passing through the exit window at the second end region are angled outwardly. At least a portion of the electrons angled outwardly through the second end region are directed beyond the outer perimeter. The electron generator is positioned within the vacuum chamber relative to the exit window in a manner to form flat electrical field lines near the central region of the exit window and curved electrical field lines near the first and second end regions of the exit window. The flat electrical field lines direct electrons through the central region in a perpendicular relation to the exit window and the curved electrical field lines direct electrons through the first and second end regions at outward angles. The exit window has window openings for allowing passage of electrons therethrough. The window openings near the first and second end regions of the exit window are angled outwardly for facilitating the passage of outwardly angled electrons. In this manner, the present invention electron accelerator is able to generate an electron beam that is wider than the width of the accelerator.
Preferably the electron generator includes at least one filament for generating electrons. A filament housing surrounds the at least one filament and has a series of housing openings formed in the filament housing between the at least one filament and the exit window for allowing the electrons to accelerate from the at least one filament out through the exit window. The housing openings are preferably configured to allow higher concentrations of electrons to exit regions of the filament housing associated with the first and second end regions of the exit window than through the central region. In one preferred embodiment, the housing openings include central and outer housing openings. The outer housing openings provide greater open regions than the central housing openings. In another preferred embodiment, the housing openings include elongate slots.
One embodiment of the invention provides an electron accelerator system including a first electron accelerator capable of generating a first electron beam having a portion extending laterally beyond the first electron accelerator. A second electron accelerator is positioned adjacent to the first electron accelerator along a common axis. The second electron accelerator is capable of generating a second electron beam having a portion extending laterally beyond the second electron accelerator to overlap along said axis with the portion of the first electron beam extending laterally beyond the first electron accelerator.
In preferred embodiments, the first and second electron accelerators are each constructed in the manner previously described above.
In one embodiment, an electron accelerator system is adapted for a sheet-fed machine including a rotating transfer cylinder for receiving a sheet of material. The transfer cylinder has a holding device for holding the sheet against the transfer cylinder. An electron accelerator is spaced apart from the transfer cylinder for irradiating the sheet with an electron beam.
In preferred embodiments, a pair of inwardly skewed rollers contact and hold the sheet against the rotating transfer cylinder. The electron accelerator and at least a portion of the transfer cylinder are enclosed within an enclosure. An inert gas source is coupled to the enclosure to fill the enclosure with inert gas. An ultrasonic device can be mounted to the enclosure for vibrating gases against the sheet to tightly force the sheet against the transfer cylinder. In addition, a blower can be mounted to the enclosure for forcing the sheet against the transfer cylinder.
In another embodiment, a system is adapted for irradiating a continuously moving web. The web travels from a pair of upstream pinch rollers to a downstream roller. The system includes an electron accelerator system for irradiating the web with an electron beam. An enclosure substantially encloses the web between the upstream pinch rollers and the downstream roller. The enclosure has an upstream shield positioned close to the upstream pinch rollers and a downstream shield positioned close to the downstream roller. An inert gas source is coupled to the enclosure to fill the enclosure with inert gas. The upstream and downstream shields are positioned sufficiently close to the upstream pinch rollers and downstream roller to prevent substantial inert gas from escaping the enclosure. The upstream pinch rollers block air from the web as the web enters the enclosure such that substantial intrusion of air into the enclosure is prevented.
In preferred embodiments, the electron accelerator system includes at least one electron beam device positioned within a module enclosure to form an electron beam module which is mounted to the web enclosure. In high speed applications, the electron accelerator system may include more than one electron beam module mounted in series along the web enclosure.
In still another embodiment, a system is adapted for irradiating a continuously moving web. An electron accelerator irradiates the web with an electron beam. An enclosure encloses the electron accelerator and a portion of the web. A series of ultrasonic members are positioned within the enclosure. The web travels over the ultrasonic members and is redirected within the enclosure. The enclosure has an entrance and an exit for the web which are out of direct alignment with the electron accelerator to prevent the escape of radiation from the enclosure.
Another embodiment of the invention provides an electron gun including a filament for generating electrons. The filament is surrounded by a housing. The housing has at least one elongate slot extending parallel to the filament along a substantial length of the filament. Preferably the electron gun includes two filaments with the housing having a total of six slots, three slots being associated with each filament. The width of each slot preferably becomes greater at the ends.